2.1. Microbial Surface Active Agents
Numerous microorganisms can multiply by using hydrocarbons as a primary carbon source. Because of the immiscibility of hydrocarbons with the aqueous environment, these microorganisms produce surface active and/or emulsifying agents that convert the insoluble, oily substrates into fine oil-in-water emulsions. The result is a marked increase in the effective hydrocarbon surface area, through which far more effective assimilation and metabolism may occur.
Among the microbes with this ability is Mycobacterium rhodochrous NCIB 9905, which Holdom et al. [J. Appl. Bacteriol. 32, 448 (1969)] showed produces a nonionic surface active agent during growth on n-decane. Iguchi et al. [Agric. Biol. Chem. 33, 1657 (1969)] found that Candida petrophilium produced a surface active agent consisting of peptides and fatty acid residues, while Suzuki et al. [Agric. Biol. Chem. 33, 1619 (1969)] reported that trehalose lipid appeared in the oil phase of cultures of various Arthrobacter, Brevibacterium, Corynebacterium and Norcardia strains. Wagner has reported the production of trehalose lipids by Norcardia rhodochrous and Mycobacterium phlei and their use in oil recovery [U.S. Pat. Nos. 4,392,892 and 4,286,660].
Torulopsis gropengiesseri was found to produce a sophorose lipid, while rhamnolipids are reported by K. Hisatsuka et al. [Agric. Biol. Chem., 35, 686 (1971)] to have been produced by Pseudomonas aeruginosa strain S7B1 and by S. Itoh et al. [Agric. Biol. Chem., 36, 2233 (1971)] to have been produced by another P. aeruginosa strain, KY4025. The growth of Corynebacterium hydrocarboclastus on kerosene was reported by J. E. Zajic and his associates [Dev. Ind. Microbiol., 12, 87 (1971); Biotechnol. Bioeng., 14, 331 (1972); Chemosphere 1, 51 (1972); Crit. Rev. Microbiol, 5, 39; U.S. Pat. No. 3,997,398] to produce an extracellular heteropolysaccharide which, among other properties, emulsified kerosene, Bunker C fuel oil and other fuel oils.
Gutnick et al. showed that Acinetobacter sp. ATCC 31012 (RAG-1) produces polyanionic protein-associated lipopolysaccharide biopolymers with strong activity as emulsion stabilizers. These interfacially active agents, collectively called emulsans, encapsulate the bacteria and are also released to the surrounding medium. The growth of Acinetobacter sp. ATCC 31012 on ethanol or on fatty acid salts produces .alpha.-emulsans [U.S. Pat. Nos. 4,230,801; 4,234,689 and 4,395,354], while the use of crude oil or hexadecane as a carbon source leads to the production of .beta.-emulsans [U.S. Pat. No. 3,941,692]. The .alpha.-emulsans and .beta.-emulsans can be derivatized to an O-deacylated form called .psi.-emulsans [U.S. Pat. No. 4,380,504]. The .alpha.-emulsans, .beta.-emulsans and .psi.-emulsans can be deproteinized to yield apo-.alpha.-emulsans, apo-.beta.-emulsans and apo-.psi.-emulsans, respectively [U.S. Pat. Nos. 4,311,830; 4,311,829 and 4,311,831, respectively].
The emulsion-stabilizing properties of emulsans have recently been applied to the utilization of highly viscous hydrocarbons by Hayes et al. [U.S. patent application temporary Ser. No. 547,892] who demonstrated that emulsans can be used in conjunction with chemical surfactants to convert heavy crude oils to low visocity oil-in-water emulsions. Such emulsan-stabilized emulsions are exceptionally stable and thus suitable for transport by truck, tanker, or conventional pipeline technology.